In large fires water alone is often inadequate for extinguishing the fire. To overcome this, water and fire-extinguishing foam mixtures have been developed that provide enhanced fire extinguishing capability when compared to plain water. These fire extinguishing foams require specialized nozzles for mixing together water and a foam solution for maximum effect.
A foam-applying nozzle typically utilizes a mixing eductor having a generally hollow body with an input opening and an opposing, spaced-apart output opening. A pressurized jet of water is directed into the input opening, creating a low-pressure area at the input opening that acts to draw a foam solution, which is coupled to the body, into the input opening. The foam solution mixes with the water jet in the body of the eductor, the mixed foam-water solution being ejected out of the output opening by the pressure of the water jet.
With reference to FIG. 1, a typical prior art foam-applying nozzle 10 utilizes a tubular constricting member 12 to create a single pressurized water jet 14 from a portion of a not-shown pressurized water supply that is coupled to an input opening 16. Water jet 14 creates a vacuum 18 in an eduction chamber 20 located downstream of input opening 16. The vacuum 18 draws a foam solution or concentrate 22 through a foam inlet 24 and into eduction chamber 20, where it mixes with water jet 14 to form a foam mixture 26. The foam mixture 26 exits nozzle 10 at an output opening 28 where it combines with the remaining portion of the water supply coupled to input opening 16, the remaining portion of the pressurized water supply having passed from the input opening to the output opening.
A drawback of this arrangement is that a single water jet 14 does not consistently evacuate air from eduction chamber 20. As a result, air 30 can enter into eduction chamber 20 faster than the single water jet 14 can evacuate it, particularly when the foam-applying nozzle 10 is adjusted for certain settings, such as a wide “fog-spray” setting. Air 30 thus limits the flow rate of the foam-applying nozzle 10. In this state the foam solution is not consistently drawn into the eduction chamber 20 and mixed with the water jet 14.
What is needed is a foam-applying nozzle that consistently draws foam solution to generate a consistent foam mixture, over a range of nozzle settings.